Average Force of meteor

1. The problem statement, all variables and given/known data
A meteor with a mass of 1 kg moving at 20 km/s collides with Jupiter's atmosphere. The meteor penetrates 100 km into the atmosphere and disintegrates. What is the average force on the meteor once it enters Jupiter's atmosphere? (Note: ignore gravity).

2. Relevant equations

K = 1/2 mv^2
W = F x d

3. The attempt at a solution

I initially started this problem with F = ma in mind. I then solved for time using d = vt and got 200 seconds. Then I found acceleration using V = Vi + at and got 100 m/s^2. By plugging in 100 m/x^2 into F=ma, I get (1 kg)(100 m/s^2) = 100 N.

The correct answer is 2 x 10^5. What am I doing wrong? Can't this problem be solved without using kinetics and work?

I am so sorry, yes, the correct answer is 2 s 10^3. Sorry to confuse everyone. Okay, so to clarify, I cannot use d =vt if it is assumed an object does not have constant velocity. Also, when acceleration is not constant, kinematic equations cannot be used.

Would it be safe to say that in situations like the problem, to use energy and work formulas?

Also, 100km = 100 km x 1000 m/1 km = 100,000 m. I stand corrected. I think I did this conversion correct and perhaps should keep it in scientific notation for a standardized test.

So just to clarify; in free fall motion, kinematic equations are used because the acceleration of gravity is constant but velocity constantly changes. In other words, to use kinematics, either velocity or acceleration must be constant. Similarly, the equation d =vt can be used for problems where there is no change in velocity. Am I on the right track?

So just to clarify; in free fall motion, kinematic equations are used because the acceleration of gravity is constant but velocity constantly changes.

Yes, because the acceleration of gravity is approximately constant near the surface of the Earth.
(It is also approximately constant in other similar situations where the distances involved are small in comparison with the distance of the gravitation).

[edit: Also free fall questions that use those equations equation ignore air resistance (they call it negligable). In this situation, though, the forces of the atmosphere are not negligable, on the contrary, they are the basis of this problem.]

In other words, to use kinematics, either velocity or acceleration must be constant. Similarly, the equation d =vt can be used for problems where there is no change in velocity.

Yes, to use those specific equations requires constant acceleration, because those equations were derived with the assumption that acceleration is constant.

Similarly, d=vt applies to constant velocities, because that equation was "derived" with the assumption of constant velocity. (I don't know if that equation is technically "derived" because it's just a rearrangement of the definition of velocity)

BUT, those equations can be used when dealing with averages. This is because the definition of "average" is essentially "the constant that has the same result" (if that doesn't make sense don't worry about it, it's just the way I think of averages).

For example:
"Average speed" is the speed that has the same result (distance travelled) as the "actual speed" (which is non-constant)
In this example, it only makes sense to speak of average speed over a certain time period

You can also look at averages in terms of totals.
For example, average speed is the Total Distance over the Total Time

But at any rate, an average is essentially a constant, and so you can use such equations.

Side note:
If something is constant, then the average is the same thing as the "actual"

Would it be safe to say that in situations like the problem, to use energy and work formulas?

You can also use your original method (what I call the "acceleration method"). See my above post for details.
In fact, I would personally suggest only using the "energy method" if you already understand the "acceleration method" because the "energy method" is essentially just a shortcut that is based off the "acceleration method" (No use using a shortcut if you don't understand how it works.)

Well, the problem says to "ignore gravity" which in my interpretation, means that acceleration is constant. I will go back and review the mistakes I made. It looks like I totally messed up an easy conversion from km->m. This thread clarified so much! Thank you everyone!